At present, a panel display structure is generally adopted in a display unit used for characters, images, videos and interaction interface. The panel display structures, such as electro fluidic display system (EFD), electrophoretic display system, in-plane switching (IPS), electro-osmosis display system and liquid crystal display (LCD), are widely used in the field. A part of the display structures adopts reflection display, for example, EFD applied to E ink or electronic paper. The EFD is also called as electrowetting display, where the electrowetting refers to a phenomenon that the wettability of droplets on the substrate is changed, i.e., a contact angle is changed to deform and shift the droplets, by varying a voltage between the droplets and the insulating substrate. By wetting it refers to a process that one fluid on a solid surface is replaced by another fluid. Liquid can spread on the solid surface, and the solid-liquid contact surface has a tendency of expanding, i.e., the adhesive force of the liquid to the solid surface is larger than its cohesive force, which is wetting. Non-wetting refers to the liquid cannot spread on the solid surface and the contact surface has a tendency of shrinking into a sphere, i.e., non-wetting is the result of the adhesive force of the liquid to the solid surface is smaller than its cohesive force. The wetting effect of a water-resistant surface can be changed by voltage (so it can be called electrowetting) to make the surface more hydrophilic (wetter). Since the originally hydrophobic surface becomes more hydrophilic now, the form of the inert liquid, for example an oil layer, which well contact with the hydrophobic surface has to be changed. Such interaction attribute control is the basis for the application of electrowetting. The application of electrowetting principle is described in detailed in publication document WO03071347 and the content issued in paper 425383385 of the publication Nature. Referring to the principle structure diagram of wetting as shown in FIG. 1, when the electrode is applied with voltage V, charges are accumulated at the lower surface of the water layer, then its electrostatic force Fel overcomes the capacitance force Fcap and breaks through the oil layer, and the hydrophobic coating on the substrate is covered, such that the water layer contacts with the original hydrophobic coating under the action of voltage. By further increasing the voltage, the oil layer broken through can be pushed to one corner of the pixel region. If the voltage is removed, the compressed oil will return to the state before the voltage is applied.
Compared with other display technologies, the EFD and its structure have many advantages, since it has both high photoelectric efficiency and switching speed. The EFD unit is a variable aperture filter in nature. In on-state driven by voltage, its visual appearance depends on the reflection material displayed when the color oil layer is faded. A good reflection material can provide a better diffuse reflection effect for a display unit to restore a simulation effect that a user reads on a paper, meanwhile a better contrast ratio can also be provided.
In the existing electronic paper, as a transverse drive principle is required for implementing the transparent EPD, Al and Ag coatings are usually applied to bottom glass layer in a transparent display to form a mirror surface or a reflection surface, which greatly differs from a real paper.
The display screens realizing the paper simulation effects in market at present involve E ink or electronic paper display screens from Sony, Amazon kindle and the like, which are based on the EPD principle, and generally on the vertical or longitudinal drive principle based on the EPD, i.e., they are implemented as a reflection (non transparent) display system. The paper effect is realized by forming a coating on the substrate using a vacuum coating process, for example spraying TiO2 particles. The TiO2 coating process is to approximate to paper effect as much as possible, but it leads to low reflection ratio, unsatisfactory contrast ratio and high cost.